For hybrid vehicles or electric-powered vehicles, storage-battery elements connected in series are employed, whose total voltage is used for the traction of the vehicle with the aid of an electric motor. Because of, for example, different internal resistances, in such serial storage-battery systems, individual battery elements are loaded more strongly than others, and are therefore subject to a faster aging process. Also, owing to the series connection, the already weakened battery elements are subject to a greater loading due to the series connection.
The overall state is ascertained by measuring the respective cell voltages as well as the total current of the storage-battery system in order, together with the measured temperature of the individual battery elements, to deduce a specific state of the individual battery elements. In particular, the state may be represented by models, the models obtaining measuring data such as temperature, cell voltage and cell current, and based on storage-battery properties which are simulated by the model, the model is able to provide a state of charge, an instantaneous resistance or an instantaneous capacity. To this end, the model may use internal variables, e.g., internal states of the battery elements such as concentrations, internal temperatures or their distributions, or state of charge or usable capacity.
For example, in order to ascertain the still-remaining traveling range of a vehicle which is operated with such a storage-battery system, conventionally, the sum of all states of the individual battery elements is used, in order to be able to deduce the energy still remaining which can be applied in total by the storage-battery system. In so doing, it is customary that the individual state parameters of all elements are combined equally with each other, that is, are averaged or provided by a sum which indicates the traction energy still remaining or other state parameters of the total storage-battery system. From this averaged or summed-up data of all battery elements, for example, a power of the storage-battery system still maximally obtainable is calculated, as well.
For that purpose, first of all, it is necessary that the state parameters of each individual cell be calculated, which means a multitude of instances of the underlying model must be provided and must be supplied with individual measurement data. Secondly, not all states important for the storage-battery system are determined by the averaging; in particular, weak battery elements are treated the same as strong battery elements.
Therefore, conventional methods for determining a maximum obtainable power do not reflect all states of the storage-battery system. Furthermore, conventional methods require a very complicated calculation, which provides an individual state monitoring/state tracking equally for all elements. In addition, already weakened cells continue to be loaded above average.
An object of the present invention is to provide a simplified mechanism for determining the states of a storage-battery system, while at the same time, the states represented more precisely reflect the instantaneous properties of the storage-battery system.